1. Technical Field of the Invention
The invention relates generally to communication systems; and, more particularly, it relates to divider circuitry, such as can be implemented within local oscillator generators (LOGENs), employed within communication devices employed within such communication systems.
2. Description of Related Art
Communication systems are known to support wireless and wire lined communications between wireless and/or wire lined communication devices. Such communication systems range from national and/or international cellular telephone systems to the Internet to point-to-point in-home wireless networks. Each type of communication system is constructed, and hence operates, in accordance with one or more communication standards. For instance, wireless communication systems may operate in accordance with one or more standards including, but not limited to, IEEE 802.11, Bluetooth, advanced mobile phone services (AMPS), digital AMPS, global system for mobile communications (GSM), code division multiple access (CDMA), local multi-point distribution systems (LMDS), multi-channel-multi-point distribution systems (MMDS), radio frequency identification (RFID), Enhanced Data rates for GSM Evolution (EDGE), General Packet Radio Service (GPRS), and/or variations thereof.
Depending on the type of wireless communication system, a wireless communication device, such as a cellular telephone, two-way radio, personal digital assistant (PDA), personal computer (PC), laptop computer, home entertainment equipment, RFID reader, RFID tag, et cetera, communicates directly or indirectly with other wireless communication devices. For direct communications (also known as point-to-point communications), the participating wireless communication devices tune their receivers and transmitters to the same channel or channels (e.g., one of the plurality of radio frequency (RF) carriers of the wireless communication system or a particular RF frequency for some systems) and communicate over that channel(s). For indirect wireless communications, each wireless communication device communicates directly with an associated base station (e.g., for cellular services) and/or an associated access point (e.g., for an in-home or in-building wireless network) via an assigned channel. To complete a communication connection between the wireless communication devices, the associated base stations and/or associated access points communicate with each other directly, via a system controller, via the public switch telephone network, via the Internet, and/or via some other wide area network.
For each wireless communication device to participate in wireless communications, it includes a built-in radio transceiver (i.e., receiver and transmitter) or is coupled to an associated radio transceiver (e.g., a station for in-home and/or in-building wireless communication networks, RF modem, etc.). As is known, the receiver is coupled to an antenna and includes a low noise amplifier, one or more intermediate frequency stages, a filtering stage, and a data recovery stage. The low noise amplifier receives inbound RF signals via the antenna and amplifies then. The one or more intermediate frequency stages mix the amplified RF signals with one or more local oscillations to convert the amplified RF signal into baseband signals or intermediate frequency (IF) signals. The filtering stage filters the baseband signals or the IF signals to attenuate unwanted out of band signals to produce filtered signals. The data recovery stage recovers raw data from the filtered signals in accordance with the particular wireless communication standard.
As is also known, the transmitter includes a data modulation stage, one or more intermediate frequency stages, and a power amplifier. The data modulation stage converts raw data into baseband signals in accordance with a particular wireless communication standard. The one or more intermediate frequency stages mix the baseband signals with one or more local oscillations to produce RF signals. The power amplifier amplifies the RF signals prior to transmission via an antenna.
While transmitters generally include a data modulation stage, one or more IF stages, and a power amplifier, the particular implementation of these elements is dependent upon the data modulation scheme of the standard being supported by the transceiver. For example, if the baseband modulation scheme is Gaussian Minimum Shift Keying (GMSK), the data modulation stage functions to convert digital words into quadrature modulation symbols, which have a constant amplitude and varying phases. The IF stage includes a phase locked loop (PLL) that generates an oscillation at a desired RF frequency, which is modulated based on the varying phases produced by the data modulation stage. The phase modulated RF signal is then amplified by the power amplifier in accordance with a transmit power level setting to produce a phase modulated RF signal.
As another example, if the data modulation scheme is 8-PSK (phase shift keying), the data modulation stage functions to convert digital words into symbols having varying amplitudes and varying phases. The IF stage includes a phase locked loop (PLL) that generates an oscillation at a desired RF frequency, which is modulated based on the varying phases produced by the data modulation stage. The phase modulated RF signal is then amplified by the power amplifier in accordance with the varying amplitudes to produce a phase and amplitude modulated RF signal.
As yet another example, if the data modulation scheme is x-QAM (16, 64, 128, 256 quadrature amplitude modulation), the data modulation stage functions to convert digital words into Cartesian coordinate symbols (e.g., having an in-phase signal component and a quadrature signal component). The IF stage includes mixers that mix the in-phase signal component with an in-phase local oscillation and mix the quadrature signal component with a quadrature local oscillation to produce two mixed signals. The mixed signals are summed together and filtered to produce an RF signal that is subsequently amplified by a power amplifier.
As the desire for wireless communication devices to support multiple standards continues, recent trends include the desire to integrate more functions on to a single chip. However, such desires have gone unrealized when it comes to implementing baseband and RF on the same chip for multiple wireless communication standards. In addition, many components and/or modules within the components employed within such communication devices and wireless communication devices include many off-chip elements.
Within many communication devices, there can be a need to perform processing of various signals (e.g., multiplication, division, addition, and/or subtraction). In some instances, a single signal (or variants generated there from) can be employed by different components, modules, and/or functional blocks within such a communication device.
Within certain communication devices and applications, there are varying design requirements related to noise (e.g., phase noise). Certain prior art approaches to performing processing of such signals within communication devices do not provide a sufficiently low degree of phase noise. In addition, many of the prior art approaches to performing processing of such signals within communication devices are inherently space consumptive and oftentimes consequently have higher production costs.
FIG. 5 and FIG. 6 are diagrams illustrating prior art approaches 500 and 600 to performing voltage division.
Referring to FIG. 5, a differential input signal in/ip is provided to AC coupling capacitors to generate a differential input voltage at the gates of the depicted devices. The differential input voltage is provided to the gates of four n-channel metal oxide semiconductor field-effect transistors (N-MOSFETs) implemented across a bottom row of the FIG. 5. The gates of two of these N-MOSFETs are coupled together, and the gates of the other two of these N-MOSFETs are coupled together. Also, as can be seen in the diagram, the sources of two of these N-MOSFETs are coupled together, and the sources of the other two of these N-MOSFETs are coupled together.
Two resistors (Rin and Rip) are coupled between a power supply voltage (shown as Vdd1) and the drains of a first pair of n-channel metal oxide semiconductor field-effect transistors (N-MOSFETs). The sources of these two N-MOSFETs are coupled together and also coupled to the source of one of the N-MOSFETs of the bottom row of the FIG. 5.
A second pair of N-MOSFETs is implemented such that the drain of one N-MOSFET of the second pair and a gate of the other N-MOSFET of the second pair are coupled to a drain of the N-MOSFET of the first pair that is also coupled to the resistor Rip. The drain of the other N-MOSFET of the second pair and a gate of the other N-MOSFET of the second pair are coupled to a drain of the N-MOSFET of the first pair that is also coupled to the resistor Rin. The sources of the N-MOSFETs of the second pair are also coupled together and also coupled to the source of one of the N-MOSFETs of the bottom row of the FIG. 5.
Two resistors (Rqn and Rqp) are coupled between the power supply voltage (shown as Vdd1) and the drains of a third pair of n-channel metal oxide semiconductor field-effect transistors (N-MOSFETs). The sources of these two N-MOSFETs are coupled together and also coupled to the source of one of the N-MOSFETs of the bottom row of the FIG. 5.
A fourth pair of N-MOSFETs is implemented such that the drain of one N-MOSFET of the fourth pair and a gate of the other N-MOSFET of the fourth pair are coupled to a drain of the N-MOSFET of the third pair that is also coupled to the resistor Rqp. The drain of the other N-MOSFET of the fourth pair and a gate of the other N-MOSFET of the fourth pair are coupled to a drain of the N-MOSFET of the third pair that is also coupled to the resistor Rqn. The sources of the N-MOSFETs of the fourth pair are also coupled together and also coupled to the source of one of the N-MOSFETs of the bottom row of the FIG. 5.
Two separate differential output voltages are provided within the FIG. 5, shown as oin/oip and oqn/oqp. These two separate differential output voltages can be viewed as being in-phase and quadrature voltage signals, respectively.
Referring to FIG. 6, this prior art embodiment includes the use of transmission gates that are depicted using dashed lines. Pair of p-channel metal oxide semiconductor field-effect transistors (P-MOSFETs) and N-MOSFETs are employed as depicted in the diagram, such that four transmission gates are implemented between each stage of P-MOSFETs and N-MOSFETs. A top row and a second row from top include pairs of P-MOSFETs. A bottom row and a second row from bottom include pairs of N-MOSFETs.
From certain perspectives, the prior art embodiment of FIG. 6 can be viewed as being a digital version of the prior art embodiment of FIG. 5. This digital version in the FIG. 6 is a complementary metal-oxide-semiconductor (CMOS) implementation, in that it has no DC current dissipation once the start up transients have passed.